Barrick has developed and patented a new flotation process that can produce copper concentrates from copper or copper-gold ores using salt or brackish water. The new process, an air-metabisulfite treatment, does not require lime or cyanide. The innovation, which Barrick hopes to license, could help reduce the mining industry's use of fresh water, which is significant because many new mineral deposits are located in arid climates where fresh water is limited.
"This is a new alternative that could have important economic and social benefits," says Barun Gorain, Director of Barrick's Strategic Technology Solutions Group. "It's cheaper and more efficient than conventional flotation methods and, because it uses sea water or brackish water, mining companies that adopt this process don't have to look for fresh water sources and risk coming into conflict with community needs."
We tried lots of things… nothing worked. Eventually, after a thorough investigation and lots of research, we finally had a breakthrough.
Flotation is a mineral processing method used to separate and concentrate valuable minerals contained in ore. In the conventional flotation process, which has been used for decades, finely ground ore is mixed with fresh water and chemical reagents to form a slurry. The slurry is pumped into a large tank and valuable mineral particles are floated to the surface via air bubbles, while waste particles sink to the bottom of the tank. Cyanide is one of the reagents used in the conventional process, along with lime. The reagents control acidity levels in the slurry and facilitate the depression of some sulfide minerals that contaminate the copper concentrates.
Nearly 10 years ago, Barrick and its partners were evaluating the use of conventional flotation at the Reko Diq copper-gold project in Pakistan. The only water source in the area was brackish, and initial testing using this water resulted in low copper recoveries.
Gorain, who holds a doctorate in metallurgical engineering, was tasked with finding an alternative. "We tried lots of things, different chemistries and chemical reagents typically used in the industry," he says. "Nothing worked. Eventually, after a thorough investigation and lots of research, we finally had a breakthrough."
Gorain was familiar with metabisulfite, a chemical reagent that is sometimes used in the zinc industry. Investigations pointed towards the benefits of using metabisulfite for flotation at Reko Diq.
The air-metabisulfite process consists of two stages. In the initial aeration stage, oxygen is pumped into a flotation tank, which begins the process of separating waste particles, most notably pyrite, from the valuable minerals in the slurry. In the second stage, metabisulfite is injected, accelerating this separation process. The aeration is believed to oxidize the surface of valuable minerals, increasing their floatability, according to Barrick's air-metabisulfite patent. The metabisulfite, which is always added to the slurry after aeration, is believed to optimize depression of waste materials, which are sent to tailings.
The process was rigorously tested in a laboratory setting. Gorain and his team found that the process works for various gold and copper ores using sea or brackish water. Of note, testing also found that copper recoveries using the air-metabisulfite process were about six percent higher on average than the conventional flotation method for the Reko Diq project.
The higher recovery rates, and the fact that the flotation process at Reko Diq would not have required lime and cyanide, would have added significant value over the life of the mine had it proceeded.
"This was a real eye opener," Gorain says.
The air-metabisulfite process is being used successfully by Antofagasta Minerals at its Esperanza copper mine in Chile's Atacama Desert. Antofagasta was Barrick's joint-venture partner at Reko Diq, and last year it purchased a 50-percent interest in Barrick's Zaldivar copper mine in Chile. The companies enjoy a close relationship, and Barrick, which owns the rights to the air-metabisulfite technology, agreed to allow Antofagasta to use the technology at Esperanza and other new projects. This will allow Barrick to observe the process in use on a commercial scale.
Last October, Barrick began using the air-metabisulfate process at the Jabal Sayid copper mine in Saudi Arabia. However, because water is so scarce in the region, the operation—a joint venture between Barrick and Ma'aden, a Saudi Arabian state mining company—uses treated sewer water for its flotation process. It is the only mine in the world that uses treated sewer water for flotation. The mine, which shipped 5.5 million pounds of concentrate for smelting in late December, expects to ramp up its annual production to 100 million pounds by the second half of 2017.
Barrick's air-metabisulfate process could also have applicability at other company properties that are currently in the project phase, such as the Pascua-Lama project. The technology is also being investigated for use with Nevada gold ores, Gorain says, noting that the process can also be used with other base metals such as zinc, silver and molybdenum. Some companies have expressed interest in licensing the technology, he says.
Many communities are becoming more assertive about water rights, Gorain says, while government restrictions on the use of fresh water are increasing. Meanwhile, new mineral deposits tend to be of lower grade, meaning they will require more water per ton of ore to mine, he adds.
"Where will that water come from?"